1. Field of the Invention
This invention relates to microwave ovens equipped with heaters together with a magnetron, and more particularly to such microwave ovens wherein a cooking utensil disposed in a heating chamber is determined for the purpose of determination of a cooking mode and food placed on or contained in the cooking utensil is determined so that heating is automatically executed in accordance with the determined cooking mode and the determined food.
2. Description of the Prior Art
Multi-function type microwave ovens have recently been commercially provided. The multi-function type microwave oven is equipped with an oven heater and a grill heater together with a magnetron, and cooking can be executed in a number of cooking modes. These cooking modes are roughly classified into a microwave cooking mode wherein food is heated by means of microwaves and a heater cooking mode wherein the food is heated by either heater. The microwave cooking mode is classified into a warming mode, a thawing mode wherein frozen raw food is thawed, and a pot-used cooking mode wherein an exclusive pot is used for the cooking. The heater cooking mode is classified into an oven mode wherein an atmosphere in the heating chamber is heated to a high temperature for the cooking and a grill mode wherein radiant heat generated by the heater is employed for the cooking.
The above-described multi-function type microwave oven is provided with an automatic cooking function. In the automatic cooking, a user operates one of a plurality of switches to select a desired cooking mode in accordance with cooking contents. Then, when desired one of a number of cooking menus is selected by operation of a switch, an incorporated microcomputer operates to automatically execute the cooking on the basis of a cooking menu program in accordance with the selected cooking mode and the selected cooking menu.
In the conventional multi-function type microwave oven, however, the user needs to selectively operate one of the switches to select the desired cooking mode and he or she further needs to operate one of the switches to select the desired cooking menu. Thus, the operation for selection of the desired cooking mode and the desired cooking menu is troublesome.
Furthermore, mistakes in selection of the switch could occur since a number of switches are provided. Cooking utensils are specified for every cooking mode. Accordingly, when a mistake in selection of the cooking mode occurs, for example, when the microwave cooking mode is mistakenly selected for the oven cooking with a metal top plate, the microwaves are supplied to the heating chamber, where sparks occur around the metal top plate.
Furthermore, in the case where the oven cooking mode is mistakenly selected when the food contained in a plastic receptacle is warmed by way of microwaves, the plastic receptacle would be melted. On the other hand, mistakes in selection of the cooking menu could occur. In this case, a desirable cooking cannot be performed.
Japanese Published Utility Model Registration Application (Kokai) No. 63-60805 discloses a technique for preventing the mistake in selecting the cooking mode such as described above. In this publication, it is determined which the cooking utensil disposed in the heating chamber is, a cooking gridiron used in the grill cooking or a thawing gridiron used in the thawing. In case that the thawing mode is mistakenly selected in the use of the cooking gridiron or that the grill mode is selected in the use of the thawing gridiron, the mistake is informed by a speaker. However, this publication relates to alarming in the case of mistake in selection of the cooking mode but does not disclose reduction in the number of the operation switches for prevention of the mistake in the cooking mode selecting operation.
Japanese Published Patent Application (Kokoku) Nos. 3-49006 and 4-38116 disclose the technique for reducing the number of switches in the microwave oven of the above-described type. In these publications, cooking menus of "GRATIN" and "BROILED SALTED FISH" in the grill cooking are determined on the basis of output changes of a sensor sensing a used receptacle and the heating is automatically controlled so that an optimum finishing can be obtained. Furthermore, in another Japanese Published Patent Application (Kokoku) No. 61-61514, a gas sensor and a thermal element are provided so that setting keys for respective kinds of cooking modes in the warming cooking in the microwave cooking are eliminated, and a control device determines the kind of food on the basis of rate of change with time in an output signal of the gas sensor after initiation of the heating. The magnetron is deenergized when the output signals of the gas sensor and the thermal element reach predetermined levels respectively.
The above-mentioned publications disclose only determination of the desired cooking menu in the warming mode in the grill cooking or the microwave cooking. However, these publications do not disclose the automatic determination of the desired cooking mode in the multi-function type microwave oven provided with various kinds of cooking mode such as the warming mode, thawing mode, pot-used cooking mode, oven mode and grill mode. Consequently, the troublesomeness in the cooking mode selecting operation and the mistake in the selection of the cooking mode in the multi-function type microwave oven cannot be solved by the above-mentioned publications.
On the other hand, it has been proposed to automatically select and set the desired cooking mode by determining the cooking utensil disposed in the heating chamber. However, the cooking utensils for the multi-function type microwave oven include two kinds of top plates, that is, an upper top plate and a lower top plate. The lower top plate is used exclusively in the oven cooking while the upper top plate is used both in the oven cooking and in the grill cooking. Accordingly, the determination cannot be made as to which is selected, the oven or grill mode and the range of automatic selection of the cooking modes is narrowed.